1. Field of the Invention
This invention relates generally to document handling devices, and more particularly, to an arrangement for adaptively driving a flag element of a document handling device.
2. Discussion
Document handling devices are commonly used today to quickly move and sort a variety of documents. Documents are often stacked and automatically fed from the document stack. A feeding mechanism is used to introduce each document to its document transport for processing and sorting. It is important to introduce each document singly, with consistent spacing, to permit the fastest feed rate possible while still maintaining proper document processing.
In high speed sorters, a hopper is often used to supply documents to the feeding mechanism. A device, commonly known as a flag, is used to move documents across the hopper during feeding. To create this movement, the flag applies a force to the last document in the stack.
A number of systems are commonly known for applying the flag force. One such flag driving system is a non-controllable dead weight system. This system uses potential energy derived from a constant weight that is attached to the flag by a cord or some other flexible connector to create a tension on the cord, and therefore, a force on the flag. The net result is a force transmitting from the flag onto the document stack.
A drawback of this non-controllable dead weight system is that it is not able to maximize the performance of the document handling device. Specifically, it is deficient in maintaining proper document spacing. The source of this deficiency relates to the force exerted by the flag on the document stack. For example, pushing a stack of several thousand documents requires far more force than pushing the last few documents. In this system, however, the force exerted by the flag on the document stack does not vary according to the number of documents in the stack. This inability to adequately control the force exerted on the document stack results in inconsistent spacing, thereby causing the performance of the document handling device to suffer.
A variation of the dead weight system, herein referred to as the variable dead weight system, attempts to improve the non-controllable dead weight system to maximize the performance of the document handling device. The variable dead weight system attempts to adjust the flag force by using a variable dead weight, such as a chain that falls onto a supporting surface during flag travel, attached to the flag. As the document stack is reduced and the flag moves accordingly, the chain falls onto the supporting surface, thereby reducing the flag force. Although this system can better match the flag force to the force required to move the document stack, it is still not responsive to the actual force requirements that may vary due to conditions in the document stack.
Another method of producing flag force against a document stack is to use some sort of motor arrangement. To best adapt to flag force requirements, many motor driven flag systems often use sensors to measure and adjust the flag motion and force. However, because the mechanical environment created by a feed sorter can be violent, the sensors must undergo filtering to ensure that the sensed values are accurate. Although these systems are more responsive to flag force requirements, they are complex, costly and are subject to maintenance issues. It is desirable to provide an improved mechanism that produces a flag force that is responsive to the force needed to move the document stack.
It is therefore an object of the present invention to provide an apparatus for driving a flag element capable of presenting an adjustable force for moving a document stack.
A further object of the present invention is to provide an arrangement for adaptively driving the flag element of a document handling device that is durable, reliable, and economical to produce.
Accordingly, the present invention is directed to an arrangement for adaptively driving the flag element of a document handling device, such as a document sorter. The invention uses a force generating mechanism to produce a torque on the periphery of a cam. A flexible connector that wraps around the cam is used to pull the flag element. The cam is shaped such that the force exerted on the flag element produced by constant torque varies in accordance with the size of the document stack in the hopper of the document handling device.